1. Field of the Invention
The present invention relates to reciprocating valves and more particularly to a means for removing accumulated material from an exposed portion of the stem of a reciprocating valve.
2. Description of the Prior Art
Heretofore, reciprocating valves with stems that are exposed to atmospheric conditions had a tendency to malfunction when foreign matter accumulated on the exposed valve stems and blocked movement of the valve stems into the valve bodies. The most common material that accumulated on the exposed valve stems was ice, which formed at sub-freezing temperatures during misty, rainy or snowy weather. When a valve stem was withdrawn for a long period of time, ice formed a bridge between the valve body and the valve stem. The ice, on occasions, became so massive that the valve could not be closed, resulting in a malfunction that could prove hazardous in certain applications. The problem was particularly acute with cryogenic valves where the cold from the controlled fluid traveled through the valve stem, increasing the likelihood of ice formation on the valve stem.
The most common solution to the ice problem has been to provide a means for heating the valve stem. A number of different types of heating means, such as heating coils, heat lamps and steam nozzles, have been used to prevent the formation of ice. The application of heat was not a satisfactory solution from an economic point of view, especially when one considers the present energy crisis. Additionally, the use of electric heating coils or lamps created a hazard when cryogenic material, such as liquefied natural gas, was controlled by the valve. In such cases, the heat lamps or coils required special explosion-proof housings to prevent the inadvertent ignition of gas that may leak from the valve.
Foreign matter, other than ice, also caused problems in that it was drawn into the packing material by the stem, thereby causing eventual failure of the packing and leakage about the stem.